In recent years, as substrate materials of a power semiconductor device, the introduction of new materials having a wideband gap, such as silicon carbide (SiC) has been expected. SiC, the wideband gap semiconductor has physical properties more excellent than silicon (Si), such as a high insulation breakdown field, a high saturated electron velocity, and a high thermal conductivity. The high insulation breakdown field material enables element thinning or high-concentration doping and causes a high pressure-resistant or low-resistant element to be manufactured. Further, since a bandgap is large, thermal excitation electrons can be suppressed and further, since heat radiation performance is high by the high thermal conductivity, a stable operation can be implemented at a high temperature. Therefore, when the SiC power semiconductor device is actualized, significant efficiency improvement and high-performance can be expected in various power supply and electrical apparatuses such as power transport and conversion devices, industrial power devices, and home appliances.
A process of manufacturing various power devices by using SiC for a substrate is substantially the same as the process using Si on the substrate. However, a heat treatment process is the significant difference to the above. A representative example of the heat treatment process is activation annealing after ion injection of impurities in order to control conductivity of the substrate. In the case of a Si device, activation annealing is performed at a temperature of 800 to 1200° C. Meanwhile, in the case of SiC, a temperature of 1200 to 2000° C. is required due to a material property thereof.
As an annealing apparatus suitable for SiC, for example, a resistance heating furnace disclosed in Japanese Patent Application Laid-Open Publication No. 2009-32774 is known. Further, besides the resistance heating furnace type, for example, an induction heating type annealing device disclosed in Japanese Patent Application Laid-Open Publication No. 2010-34481 is known. In addition, as a method for suppressing SiC surface roughness by annealing, a method of installing a cap for exposing SiC in a part facing a SiC substrate is disclosed in Japanese Patent Application Laid-Open Publication No. 2009-231341.